1. Field of the Invention
The present invention relates generally to the field of digital communications, and particular to communications interface circuits and power management systems and methods.
2. Related Art
Various communication interface standards are known for establishing communications between computer systems and peripheral devices. One example of such an interface is the RS-232 serial communications interface standard which is used in many applications, including IBM compatible personal computers. Other common standards include the RS-485 or RS-422 standards. Such digital communications standards include specifications adequate for equipment of different designs and manufacture to communicate with each other. Conventionally, the circuitry used to provide a computer system with RS-232 communications interface capability remains active and powered even when not connected to a device. In the past, when computer systems were generally powered via a standard electrical outlet, this constant utilization of power did not present a problem because of the virtually inexhaustible supply of power available.
However, with the recent popularity of portable laptop and palmtop computers, which generally draw power from a rechargeable battery, this unnecessary power consumption has become problematic. Without a check on the status of its connection to other systems, the unused interface circuitry continues to drain power from the rechargeable battery, thereby reducing the amount of time the portable computer system may be used remotely.
To reduce this unnecessary power consumption, and thereby extend the time the rechargeable battery remains charged, it is desirable to provide a communication interface circuit which detects when it is not coupled to another communications system, and which responds by signaling for the application of power to certain portions of the interface circuit to be suspended. It is also desirable for the interface circuit to include a power management system that monitors communication activity through the communication interface circuit. The power management system signals certain portions of the communication interface circuit to shut (or power) down if there exists no communication activity through the communication interface circuit for a prescribed period of time as well as power up in the event that communication activity is detected and the communication interface circuit is shut down.